I'm enjoying it quite a bit; combining libraries is a feature I always wanted and now that I have it I don't ever want to go back. It's been running pretty smoothly now that a few major updates have been pushed out. When I got into the closed beta, my integrations would desync quite a bit and made it a chore to reconnect them every time. Now, the only persistent issue I have is Galaxy's inability to sync play information about my games. It always give me a popup that says they were unable to load the data, though I'm not sure if this is GOG or Steam's privacy settings. Minor issues crop up occasionally; sometimes it takes a while to sync up all my libraries, and sometimes Galaxy refuses to load a library entirely until it or my PC are restarted. But these bugs are few and far between, and overall I'm happy with where it's at right now.
My main wish in terms of improvement would be fixing bugs and making the experience as smooth as silk. Bugs still occur often enough to remind me that this is in beta. Also, I'm not sure if this is possible, but a way to manage your downloads through GOG Galaxy, or at least have Galaxy be able to tell you when something is being downloaded, would be very useful. My internet is precarious, and any sort of download can immediately cripple the entire household. Currently I have to remember to check whether Steam is downloaded updates in the background, so being able to monitor and/or adjust that in GOG would be a big improvement.